This invention relates to launchers used to launch a pipeline pig or a diagnostic tool into a pipeline system. The primary purpose of a pig launcher is to launch the pig or tool into the pipeline system without interruption of the flow through that system. Pig launching (and receiving) systems vary from one to another depending on specific purpose and product. Variations include such things as placement of valves, automated mechanisms, length of the launch tube or barrel, type of closure door, and the means to move a pig into the reduced cross-section area of the barrel (e.g. gravity, screws).
Regardless of those variations, all launchers (and receivers) include the barrel, which holds one or more pigs, and a large branch connection which connects the barrel to the pipeline system. When ready to launch a pig into the pipeline system, a Tee section diverts pipeline fluid flow into the end of the barrel, behind one or more of the pigs positioned in the barrel. Because this fluid flows unabated into the barrel, it loses momentum and drops in pressure to the pressure of the barrel without doing immediate work. The fluid from this flow could be used much more aggressively to do immediate work towards launching the pig.